A new marine biogenic emission: methane sulfonamide (MSAM), DMS and DMSO<sub>2</sub> measured in air over the Arabian Sea

Abstract

<p><strong>Abstract.</strong> We present the first ambient measurements of a new marine emission methane sulfonamide (MSAM), along with dimethyl sulfide (DMS) and dimethyl sulfone (DMSO<sub>2</sub>) over the Arabian Sea. Two shipborne transects (W to E, E to W) were made during the AQABA (Air Quality and Climate Change in the Arabian Basin) measurement campaign. DMS mixing ratios were in the range 0.3–0.5 ppb during the first traverse of the Arabian Sea (first leg) and 0.1 to 0.3 ppb in the second leg. In the first leg DMSO<sub>2</sub> was always below 0.04 ppb and MSAM was close to the limit of detection. During the second leg DMSO<sub>2</sub> was between 0.04–0.12 ppb and MSAM was mostly in the range 0.02–0.05 ppb with maximum values of 0.06 ppb. An analysis of HYSPLIT back trajectories combined with calculations of the exposure of these trajectories to <i>chlorophyll a</i> content in the water revealed that most MSAM originates from the Somalia upwelling region, known for its high biological activity. This new marine emission is of particular interest as it contains both sulfur and nitrogen, making it potentially relevant to marine nutrient cycling and particle formation.</p>

Marine gas-phase sulfur emissions during an induced phytoplankton bloom

“…S6). This is surprising as MSAM was recently measured at mixing ratios of up to 60 ppt corresponding to up to 33% of DMS in upwelling areas of the Arabian Sea and was correlated with DMSO2 (r = 0.8) (Edtbauer et al, 2020).…”

“…Other sulfur species, including dimethyl disulfide, carbon disulfide, and carbonyl sulfide, have previously been measured in the seawater in highly productive regions, though in significantly smaller quantities than DMS (Kettle et al, 2001;Leck and Rodhe, 1991). Recently, a previously unobserved biogenic marine volatile sulfur molecule, methane sulfonamide, was measured in the gas-phase near an upwelling region of the Arabian Sea at mixing ratios up to 33% of DMS (Edtbauer et al, 2020). Additionally, the recent discovery of the DMS oxidation product hydroperoxymethyl thioformate (HPMTF) has prompted researchers to reexamine our understanding of the sulfur cycle (Veres et al, 2020).…”

Atmospheric gas-phase composition over the Indian Ocean

“…DMS and isoprene DMS in the Arabian Sea is projected to act as a relatively large oceanic source of sulfur to the atmosphere during the Asian summer monsoon season (Lana et al, 2011). These high emissions have been confirmed by recent ship-based measurements during the AQABA campaign, identifying elevated DMS values in the atmosphere ranging from to 500 ppt (Edtbauer et al, 2020). Given the low atmospheric background pollution and the elevated DMS mixing ratios, the latter was found among the ten most important OH sinks with a reactivity of 0.02 s 1 (Pfannerstill et al, 2019).…”

Kinetic and mechanistic study of the reaction between methane sulphonamide (CH<sub>3</sub>S(O)<sub>2</sub>NH<sub>2</sub>) and OH

“…MSAM is highly soluble and a dry deposition velocity of ≈ 1 cm s -1 to the ocean has been estimated (Edtbauer et al, 2019).…”

“…to the observations of Edtbauer et al (2019), there have been no laboratory studies to investigate either its spectroscopy or the kinetics of its reactions with atmospheric radicals, such as OH, so that its atmospheric lifetime and the products formed during its degradation in air were unknown. Crystalline MSAM melts at 363 K, has a boiling point of approximately 453 K and a vapour pressure of < 0.02 Torr at room temperature.…”